Satellite radioterminal communications systems and methods are widely used for radioterminal communications. Satellite radioterminal communications systems and methods generally employ at least one space-based component, such as one or more satellites that is/are configured to wirelessly communicate with a plurality of satellite radioterminals.
A satellite radioterminal communications system or method may utilize a single antenna pattern (i.e., a global beam) to cover an entire area served by the system. Alternatively or in addition, in cellular satellite radioterminal communications systems and methods, multiple antenna patterns (i.e., beams or cells) are provided, each of which can serve substantially distinct geographical areas in an overall service region, to collectively serve an overall satellite footprint. Thus, a cellular architecture similar to that used in conventional terrestrial cellular radioterminal systems and methods can be implemented in cellular satellite-based systems and methods. The satellite typically communicates with radioterminals over a bidirectional communications pathway, with radioterminal communication signals being communicated from the satellite to the radioterminal over a down-link, forward-link or forward service link, and from the radioterminal to the satellite over an up-link, return-link or return service link.
The overall design and operation of cellular satellite radioterminal systems and methods are well known to those having skill in the art, and need not be described further herein. Moreover, as used herein, the term “radioterminal” includes cellular and/or satellite radioterminals with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radioterminal with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and/or a pager, Internet and/or Intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver. As used herein, the term “radioterminal” also includes any other radiating user device/equipment/source that may have time-varying or fixed geographic coordinates, and may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based), or situated and/or configured to operate locally and/or in a distributed fashion at any other location(s) on earth and/or in space. A “radioterminal” also may be referred to herein as a “radiotelephone,” “terminal,” or “wireless user device”.
As is well known to those having skill in the art, terrestrial networks can enhance cellular satellite radioterminal system availability, efficiency and/or economic viability by terrestrially reusing at least some of the frequency bands that are allocated to cellular satellite radioterminal systems. In particular, it is known that it may be difficult for cellular satellite radioterminal systems to reliably serve densely populated areas, because the satellite signal may be blocked by high-rise structures and/or may not penetrate into buildings. As a result, the satellite band spectrum may be underutilized or unutilized in such areas. The use of terrestrial retransmission of all or some of the satellite band frequencies can reduce or eliminate this problem.
Moreover, the capacity of the overall system can be increased significantly by the introduction of terrestrial retransmission, since terrestrial frequency reuse can be much denser than that of a satellite-only system. In fact, capacity can be enhanced where it may be mostly needed, i.e., in and/or proximate to densely populated urban, industrial, and/or commercial areas. As a result, the overall system can become much more economically viable, as it may be able to serve a much larger subscriber base. Finally, satellite radioterminals for a satellite radioterminal system having a terrestrial component within the same satellite frequency band and using substantially the same air interface for both terrestrial and satellite communications can be more cost effective and/or aesthetically appealing. Conventional dual band and/or dual mode alternatives, such as the well known Thuraya, Iridium and/or Globalstar dual mode satellite and/or terrestrial radiotelephone systems, may duplicate some components, which may lead to increased cost, size and/or weight of the radioterminal.
U.S. Pat. No. 6,684,057 issued Jan. 27, 2004, to the present inventor Karabinis, and entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that a satellite radioterminal frequency can be reused terrestrially by an ancillary terrestrial network even within the same satellite cell, using interference cancellation techniques. In particular, the satellite radioterminal system according to some embodiments of U.S. Pat. No. 6,684,057 includes a space-based component that is configured to receive wireless communications from a first radioterminal in a satellite footprint over a satellite radioterminal frequency band, and an ancillary terrestrial network that is configured to receive wireless communications from a second radioterminal in the satellite footprint over the satellite radioterminal frequency band. The space-based component also receives the wireless communications from the second radioterminal in the satellite footprint over the satellite radioterminal frequency band as interference, along with the wireless communications that are received from the first radioterminal in the satellite footprint over the satellite radioterminal frequency band. An interference reducer is responsive to the space-based component and to the ancillary terrestrial network that is configured to reduce the interference from the wireless communications that are received by the space-based component from the first radioterminal in the satellite footprint over the satellite radioterminal frequency band, using the wireless communications that are received by the ancillary terrestrial network from the second radioterminal in the satellite footprint over the satellite radioterminal frequency band.
U.S. Patent Application Publication No. 2003/0054761 A1, published Mar. 20, 2003 to the present inventor Karabinis and entitled Spatial Guardbands for Terrestrial Reuse of Satellite Frequencies, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes satellite radioterminal systems that include a space-based component that is configured to provide wireless radioterminal communications in a satellite footprint over a satellite radioterminal frequency band. The satellite footprint is divided into a plurality of satellite cells, in which satellite radioterminal frequencies of the satellite radioterminal frequency band are spatially reused. An ancillary terrestrial network is configured to terrestrially reuse at least one of the ancillary radioterminal frequencies that is used in a satellite cell in the satellite footprint, outside the cell and in some embodiments separated therefrom by a spatial guardband. The spatial guardband may be sufficiently large to reduce or prevent interference between the at least one of the satellite radioterminal frequencies that is used in the satellite cell in the satellite footprint, and the at least one of the satellite radioterminal frequencies that is terrestrially reused outside the satellite cell and separated therefrom by the spatial guardband. The spatial guardband may be about half a radius of a satellite cell in width.
U.S. Patent Application Publication No. US 2003/0054815 A1, published Mar. 20, 2003 to the present inventor Karabinis, and entitled Methods and Systems for Modifying Satellite Antenna Cell Patterns in Response to Terrestrial Reuse of Satellite Frequencies, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that space-based wireless radioterminal communications are provided in a satellite footprint over a satellite radioterminal frequency band. The satellite footprint is divided into satellite cells in which satellite radioterminal frequencies of the satellite radioterminal frequency band are spatially reused. At least one of the satellite radioterminal frequencies that is assigned to a given satellite cell in the satellite footprint is terrestrially reused outside the given satellite cell. A radiation pattern of at least the given satellite cell is modified to reduce interference with the at least one of the satellite radioterminal frequencies that is terrestrially reused outside the given satellite cell.